Two of the main hypotheses put forth to explain the function of immature social play are the Social Skill Hypothesis and the Motor Training Hypothesis focussing on whether play can improve social competence to develop cooperative social networks or physical abilities to outcompete others, respectively. Here, we tested these hypotheses on a monkey species, the wild gelada (Theropithecus gelada) from the Kundi plateau, Ethiopia. This species is organized in bands divided in One-Male Units (OMUs), united only via social play. Immatures form ‘play units’ in which individuals from the same and different OMUs interact. We analysed the potential differences between inter- and intra-OMU play to verify which of the two hypotheses (Social Skill or Motor Training Hypothesis) best explains the function of play in geladas. We analysed 527 video-recorded social play sessions and found mixed support for both hypotheses. In agreement with the Social Skill Hypothesis, we found that play in geladas shows scarce social canalization being similarly distributed across age, sex and group membership. In line with the Motor Training Hypothesis, we detected higher levels of competition (shorter and more unbalanced sessions) in inter-OMU compared to intra-OMU play. Hence, in geladas play can be a tool for both the development of social relationships and the improvement of the physical skills necessary to cope with either future mates or competitors. In conclusion, neither hypothesis can be discarded and both hypotheses concur in explaining why immature geladas peculiarly form ‘play units’ embracing both ingroup and outgroup members.

用来解释未成熟社交游戏功能的两个主要假设是社交技能假说和运动训练假说，侧重于玩耍能否提高社交能力以发展合作性社交网络或身体能力胜过他人。在这里，我们在来自埃塞俄比亚昆迪高原的野生吉拉达（Theropithecus gelada）猴子物种上测试了这些假设。该物种按分为单雄单位（OMU）的乐队进行组织，仅通过社交活动进行组合。不成熟会形成“游戏单元”，来自相同和不同OMU的个体会相互作用。我们分析了OMU内部游戏和内部OMU游戏之间的潜在差异，以验证以下两个假设（社交技巧或运动训练假说（Motor Training Hypothesis）可以最好地说明游戏中的游戏功能。我们分析了527个视频记录的社交游戏会话，发现对这两种假设的支持不一。与社会技能假设相一致，我们发现在吉拉达斯玩游戏显示稀缺的社会渠道分布在年龄，性别和群体成员之间的分布相似。符合运动训练假说，与OMU内的比赛相比，我们发现OMU内的比赛水平更高（比赛时间更短，不平衡）。因此，在游戏中，游戏既可以成为发展社交关系，又可以提高应付未来伴侣或竞争对手所必需的身体技能的工具。总之，两种假设都不能被丢弃，两种假设都可以解释为什么不成熟的意式冰淇淋会特别形成“游戏单位”，既包含团内成员又包含团外成员。